1. Field of Invention
This invention relates to the extraction of geometric, dynamic, and material properties, specifically to such properties which are used for the characterization of micro- and nano-scale systems.
2. Prior Art
Precise determination of geometric, dynamic, and material properties of micro- and nano-scale systems is fundamentally important to characterizing said systems. A precisely characterized micro/nanosystem becomes an accurate sensor and or actuator for the micro/nanotechnologist. Conventional metrology methods at this scale typically yield 1 to 3 significant digits of precision. Such low precision slows advancement in the field because researchers find it difficult to accurately measure and evaluate the new micro- and nano-scale phenomena. Precise metrology of micro- and nano-scale systems is vitally needed in order to fully exploit micro- and nanotechnology. In particular, precise test and characterization methods are required to: help understand the new physical phenomena at the micro- and nano-scale; help fabrication facilities define micro- and nano-scale material for potential users; facilitate consistent evaluations of material and process properties at the required scales; and provide a basis for comparisons among materials and systems fabricated at different facilities.
Micro- and nano-scale systems typically do not look like or behave like a designer originally predicts on paper or on computer. However, several microelectromechanical systems (MEMS) have achieved commercial success. A couple of examples are the accelerometers used in car airbags, and the micromirrors used in digital light processing projectors. Of the systems that have become useful, most (if not all) of their geometric and material properties remain uncertain during their lifecycle. The reasons include the following: many systems in use today have not required precise characterization due to their intentional lack of sensitivity to design parameters for robustness; if the effective mechanical performance is less than ideal, the performance may be improved by electronic tuning if an adequate characterization-reference exists; since conventional measurement techniques typically have large uncertainties associated with them, the engineer will receive a low return on the time and cost invested in performing the measurement.
The success of a few simple microdevices should not mask the need to develop more complex systems and to better understand, model, and predict more complex physical phenomena at the micro- and nano-scale. The prerequisites for said advancement are the precise characterization of the governing geometric, dynamic, and material properties which form the parameters of linear and nonlinear analytical models and numerical models. However, because of the above reasons, and because practical measurement techniques have been largely nonexistent for micro- and nano-scale systems, most researchers are reluctant to invest in the time and cost to measure the fundamental properties of their creations. Instead, many researchers have relied on the measured properties of similarly-processed materials that have been reported in the literature or they rely on the generic material property databases found in commercial MEMS software packages. Although the reported values found in the literature pertain to a particular processing sequence that is often repeated in other laboratories, variations that are inherent to current processing techniques make it difficult to exactly reproduce the results elsewhere. These resulting variations are due to many factors which stem from the dynamics of temperature, pressure, and concentration of the reactants during processing deposition and etching. Characterization of these dynamics continues to be an active area of research. Due to the current inability to precisely control these factors and the strong sensitivity of material properties on these factors, it is also difficult to reproduce exactly the same results on a subsequent run using the same equipment and recipe. What is more, during any particular run, material properties vary from wafer to wafer. And for each wafer on any run, material properties can vary over the wafer itself.
Although there are a multitude of conventional measurement methods, they are impractical and nearly all of the methods are relatively imprecise. Unlike the invention presented herein, conventional methods suffer from one or more of the following issues: the method is too costly for most budget-conscious organizations or institution; The methods are typically single-function; that is, it often requires the use of N distinct methods to extract N distinct properties; a large amount of chip real estate is required for methods which use a large array of test structures; The measurement is typically global and unable to extract local variations in properties; The extracted measurement is a function of one or more unconfirmed properties such that significant uncertainty remains; the measurement method itself is not well-characterized or well-calibrated, such that the extracted measurement typically yields about 1 to 3 significant digits of precision; the methods are time-consuming, which is not amenable to a pace of industry; there is a lack of characterization standards at this length scale, which makes it difficult for manufacturers to specify their materials and for customers to specify their needs; many methods are destructive, which may render the surround material unusable; many methods often require subjective interpretation which introduces human error into the overall uncertainty; nearly all measurement tools are relatively large and non-portable, which limits testing to suitable laboratory facilities; many methods are difficult to use and may require specialized personnel for their operation. In such cases, the precision of measurement depends on the expertise of the operator; nearly all conventional methods are difficult to automate, which is not amenable to the pace of industry; nearly all conventional characterization methods are performed in the laboratory before the system is packaged; such methods are not amenable to post-packed testing in-the-field when conditions change; and many test structures require unique fabrication processes, which limits such methods from being generally applied.
The characterization method of the present invention does not suffer from any of the aforementioned issues. The method should be contrasted to prior methods and tools. In particular, the present invention is most closely related to U.S. Pat. No. 6,542,829. In regards to the above issues, U.S. Pat. No. 6,542,829 is subject to issue Nos. 8, 9, 12, 13, and 14; that is, the method requires the purchase of costly software, it extracts geometrical properties only, the extracted measurements are functions of unconfirmed properties, the finite-element simulation is computationally intensive, and the uncertainty in the simulated result significantly affects the uncertainty of the extracted measurement. Other examples prior art include U.S. Pat. Nos. 6,998,851; 5,786,621; 6,753,528; 6,721,094; 6,567,715. An overview of conventional characterization methods may be found in “Electro Micro-Metrology” by Jason Vaughn Clark, Ph.D. dissertation, Dec. 20, 2005, pp. 583-605, and in the “MEMS Handbook, 2nd Ed.” edited by Mohamed Gad-el-Hak, Taylor and Francis, CRC Press, 2005.
In view of the foregoing, a need exists in the art for a practical and precise method to characterize micro- and nano-scale properties, which does not suffer from any of the aforementioned problems.